A phased array antenna is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. During transmission, phased array antenna systems can use multiple individual antennas (or, in some instance, subarrays of antennas), where each antenna is separately energized in such a way that the multiple individual antenna elements cooperate to produce a transmitted electromagnetic wave that is highly directional. The relative phases and amplitudes of signals feeding the antenna elements may be varied to steer the transmitted electromagnetic wave (e.g., a radiation pattern) in a particular direction. An exemplary phased array antenna includes a plurality of active circuits spaced apart from each other by known distances. Each of the active circuits is coupled through a plurality of phase shifter circuits, amplifier circuits and/or other circuits to either or both of a transmitter and receiver. In some cases, the phase shifter, amplifier circuits and other circuits (e.g., mixer circuits) are provided in a so-called transmit/receive (T/R) module and are considered to be part of the transmitter and/or receiver.
With a phased array antenna, each individual antenna element (or sub array) radiates energy at a different phase, respectively. Thus, the phased array can produce an equi-phase beam front or cumulative wave front of electromagnetic energy that can travel in a given direction. The given direction in which the wave or beam travels depends at least in part on the differences in phase or timing of the signals activating the antenna. Similarly, when a phased array is receiving energy, the individual antennas in the phased array detect the return beams of energy, and analysis of the return beam phase helps to determine the direction of arrival of a return beam.
A phased array requires proper calibration for the signal path of each element. In some instances, the production facility performs an initial calibration of the phased array. This initial calibration can require precisely positioned measurement equipment. During the initial calibration that is part of the manufacturing process, near-field or far-field sources can be used for calibration of phased arrays. After the antenna is deployed in the field, calibration may need to be performed again to compensate for defective elements, changes in element performance over time (e.g., graceful degradation over time), environmental factors (e.g., wind, temperature, or other influencing factors), etc. Calibration in the field also may be required to change or maintain desired radiation pattern characteristics, implement changes to the antenna, and implement other changes to maintain overall antenna performance. For example, after the phased array antenna has been out in the field, one or more of the phased array elements may degrade or fail over time and may need to be replaced in the field. After repair or adjustment to the phased array, there might be a need to perform calibration of the phased array when one or more components that affect the signal path characteristics of the phased array are replaced.